Key-set circuit



July 28, 1942. J. B. McKlM 2,290,986

` KEY-SET CIRCUIT Filed Dec. 5l, 1940 6 Sheets-Sheet 2 Mmc/NAL JEMCK/M Byw A TTORNEV July Z8, 1942. J. B. MQKIM KEY-SET CIRCUIT Filed Dec. 51, 1940 6 Sheets-Shee/t 3 mem /N VEN TOR By J. B. Mc /f/M 6.31. M

A TTORNEV July 2s, 1942. L B, MCKlM 2,290,986

' KEY-SET CIRCUIT I A T 7URNEV July 28, 1942. J, B McKlM 2,290,986

' KEY-SET CIRCUIT Filed Dec. 51, 1940 6 sheets-sheet 5 JA ck.:

A TTORNE V July 23, 1942 '.1. B, McKlM 2,290,985

KEY-SET CIRCUIT Filed DeC. 5l, 1940 6 Sheets-Sheet 6 T0 ODD NLMHEREU POSITIONS WGNAL/NC CURRENT SUPPLY CIRCUIT /N VEN TOR J. B. Mc K/M Bygew A TTORNE V Patented July 28, 1942 UNITED STATES PATENT OFFICE KEY-SET cmcorr `lames B. McKim East Grange, N. J., assigner to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York This invention relates to telephone exchange systems and more particularly to systems in which connections are established between subscribers lines terminating in different offices over toll trunks by dial switching mechanism under the control of a toll operator.

In the establishment of connections to offices of a dial switching area for which toll rates should be assessed for service, it is customary for a calling subscriber in such an oiiice who desires a connection with another subscriber at a remote point to dial a number whereby a connection isrst obtained with a toll operator who then proceeds to set up the desired connection and to supervise the assessment of the required toll charge.

In some cases it is desirable to include in an exchange area offices which are located on the fringe of such area and to control the extension of toll connections to lines terminating in such oices from toll operators positions located in the main exchange area. Under these conditions, the trunks extending from the toll operators position to the fringe oces might be of considerable length and since the register sender equipment would be located in the terminating cnice, the transmission of key-pulsing impulses over such a long trunk for setting the digit registers of a selected register sender by direct current impulses strength as has heretofore been proposed, might prove to be unreliable.

It has been proposed as disclosed in the application of P. B. Murphy, Serial No. 372,560, filed ,Y concurrently herewith, to transmit digitimpulses over long trunks for registration in the registers of a sender located at a distant terminating office by providing each toll operators position circuit with a ten button key-set common to the cord circuits of the position which becomes associated with a cord circuit when the operator takes it for use; by providing equipment common to all of the operators positions for generating a plurality of alternating current frequencies, for combining such frequencies in different combinations of two frequencies each and for applying them to the keys of the key-set and to the contacts of the key-pulsing signaling relay and to the contacts of a start relay also provided at each operators position; and by providing receiving equipment associable with the terminating sender for receiving the signal impulses, for translating them and for. controlling the sender in accordance therewith.

of diii'erent polarity and current The present invention relates more particularly to key-set circuits applicable to systems of the type disclosed in the application above reierred to and has for its object to enable the more reliable andr eiiicient functioning of a toll operators position in theestablishment of toll connections to subscribers lines terminating in offices of the dial switching character.

To attain this object each operators position is provided with a ten button key-set, a start key, one or more key-pulsing keys and control relays. After the operator has extended a connection toward the terminating oflice by plugging into the jack of a trunk extending thereto she operates a key-pulsing key at her position which causes the operation of a connecting relay and a key-pulsing relay whereby a signaling circuit is established from her key-set circuit over the talking conductors of the cord circuit and the selected trunk to the receiving equipment over which circuit a preliminary key-pulsing signal of two particular frequencies generated by a signaling current supply circuit, common to all operators positions, is transmitted during the time that the key-pulsing key is depressed and for an interval thereafter as predetermined by the slowreleasing characteristic ofl the key-pulsing relay. The operation of the key-pulsing relay alsoV operates an additional key-set disconnect relay which locks under the control of a start relay to maintain the connecting relay operated until after the subsequent operation of the start relay. After the termination of the key-pulsing signal following the release of the key-pulsing relay, a lamp is lighted at the position as a'signal to the operator that she may then proceed to key the digits of the wanted line number onr the keys of her key-set.

The ten keys of the key-set are so connected to the signaling current supply circuit that the depression of different ones of such keys is instrumental in transmitting signals comprising diierent combinations of tWo frequencies each. After the operator has completed the keying of the digits of the wanted line number, she'then operates the start key of her key-set circuit which causes the operation of the start relay to apply a further combination of two of the frequencies generated by the common equipment over the trunk to the receiving equipment as a signal that she has completed the keying of all digits. The start relay upon `operating locks under the control of the key-set disconnect relay, opens the locking circuit of such disconnect f relay and closes a further locking circuit therefor which is effective so long as the start key is held depressed. When, however, the start key is released, the key-set disconnect relay releases after a time interval determined by its slow-torelease characteristic in turn releasing the start relay to discontinue the start signal and releasing the connecting relay.

The invention having been considered in a general manner, reference may now be had for a clearer understanding thereof to the following detailed description taken in connection with the accompanying drawings in which:

Figs. 1, 2 and 3, taken together, with Fig. 2 at the right of Fig. l 'and Fig. 3 beneath Fig. 2 disclose one embodiment of the invention; Fig. 2 showing one of the cord circuits of an operators position and a portion of the equipment common to all cord circuits of the position; Fig. 1 showing the grouping circuit and telephone circuit of the operators position; and Fig.r3 showing the key-set circuit of the operators position; Y

Figs. and 6 taken together with Fig. 6 beneath Fig. 5 disclose a further embodiment of the invention; Fig. 5 showing one of the cord circuits of an operators positionv and the operators position grouping and telephone circuit common to al1 cord circuits of the position; and Fig. 5 showing the key-set circuit of the'operators position; and

Fig. 4 shows trunks outgoing from the toll operators positions disclosed in Figs. 1 to 3, inclusive, and Figs. 5 and 6, and incoming at a Idistant terminating office in incoming selector switches indicated by the box in the upper right corner thereof, a link |circuit represented by the boxA so labeled, asender represented by the box solabeled and a key-impulsing receiving circuit represented by the box so labeled.

The operators position key-set circuits of Figs. Band 6 are associable with signaling current supply circuits indicated by the boxes 350 and 650 of the type fully disclosed in the application of P. B. Murphy above referred to, and in the application of L, A. Meacham, Serial No. 372,557, led Dec. 31, 1940. Toll connections may be completed by the cord -circuits of Figs. 2 and 5 by the connection thereof with trunks extending to terminating oices. For controlling the completion of connections from such trunks, terminating equipment of the type disclosed in the application of P. B. Murphy hereinbeore referred to, may be employed although it is to be understood that other types of terminating equipment arranged toV be responsive to alternating current sign-als of the type transmitted by the key-set circuits under consideration, might equally well be employed.

The embodiment of the invention disclosed in Figs.` 1 to 3, inclusive, together with Fig. 4, will rst be considered. It will be assumed that a toll connection is incoming to the operators position and that the operator answers the call on the toll line by lplugging the cord circuit plug 200 into the toll line jack She then depresses the cord key 202 to the right or talking position. A circuit is thereupon established for relay 203 extending from battery through the winding of relay 203, theA alternate contacts of keyV 202, =conductor 204 to ground at therinner lower normal contacts of relay |00 o the operators telephone circuit. Relay 203 upon operating closes a circuit lfor relay |00 extending as traced from ground on conductor 204 over the alternate contacts of key 202, the No. 1 lower front contacts of relay 203, conductor 205 to battery zthrough the winding of relay |00. Relay |00 thereupon operates removing ground from ccnductor 204 to preventanother cord circuit relay, such as relay 203, from operating. With relay |0| operated, since the operators telephone set |02 will have been plugged into the position jack to establish the circuit thereof extending from battery through its winding, the upper contacts of jack |03 to ground at the outer right back Ycontact of relay |04, relay |00 closes the holding circuit for cord circuit relay 203 which may be traced from ground over its inner lower alternate contacts, the No. 1 upper front contacts of relay |0|, conductor |05, the No. 1 upper front contacts of relay 203, the upper alternate contacts of key 202 to battery through the Winding of relay 203. Thereby relay 203 individual to the cord circuit and relay |00 common to all cord circuits of the lposition are held operated. Relay 203 splits the cord circuit and associates conductors 206 to 209,'inclfusive, with the cord circuit.

The operation of relay |00 connects Vthe tip Iand ring conductors |06V and |01 of the operators headset circuit over its outer front contacts and the No. 2 upper yand No. 1 lower contacts of relay |0| to conductors |03 and |09 extending to the -left or monitoring Lcontacts, of the key 202 and at its inner upper back contact disconnects the winding of relay ||0 from conductor If at this time the key 202 of another cord circuit of the operators position is operated to the left or monitoring position, the operator will be able to talk or listen on both cord circuits but will be able to split, transfer or keypulse on only the cord circuit, the talking key of which has been operated to the right or talking position.

Upon the operation of relay 203 a circuit is also established from high resistance ground on the sleeve of jack 20| over the sleeve of plug 200, the No. 2 lower contacts of relay 203 to battery through the windings of relays 2|0 and 2| l.

, Rel-ay 2|| upon operating closes an obvious cir- .cruit for relay 2|2, but relay 2|0 being marginal does not operate at this time. At its inner upper front contact, relay 2|2 connects ground through high resistance 2|3 and over the No. 3 lower contacts of relay 203 to the rear cord supervisory lamp 2|4 to warm the lamp without lighting it thereby improving its flashing characteristic. At its lower back contact, relay 2|2 disconnects the tip of the answering plug 200 from the busy test conductor 2|5 which is connected over the No. 4 lower front contact of relay I0| through the winding of relay |I2 to ground and through condenser ||3 toV ground through the yprimary Winding of transformer ||4 and thence inductively to the operators headset |02. At its outer front contacts, relay 2|2 also establishes a talking circuit which may be traced from the tip of the plug 200 over the No. 5 upper contacts of relay 203, conductor 205, the No. 2 upper back contact of relay 300, conductor 30|, the lower right normal rcontacts of splitting key 2|6, the lower front Contact of relay 2| 2, the lower back contact of relay 2H, conductor ||5, the lower No. 5 contacts of relay |0|, conductor |01, through the lower windings of repeating coil I I6, inductively coupled to the operators headset transmitter, and over the back contacts of relay ||0 to the operators headset receiver, thence returning over conductor |05, the No. 3 upper contacts of relay |0|, conductor the upper back contact of relay 2||, the upper front. oontact of relay 2 l2, the upper right normal contacts of splitting key 2|.3, conductor 342, the No. 3 lower back contact of relay 300, conductor 209, the No. 5 lower .contacts of relay 233 to the ring of plug 269. The operator is now enabled to receive instructions over the toll trunk for the further extension of the connection.

Having received instructions and it being assumed that a connection is desired with a subscribers line which terminates in a dial switching oflice accessible over a group of trunks of which one is disclosed in the upper portion of Fig. 4, the operator proceeds to test such trunks by touching the tip of plug 224 to the sleeves of the trunk jacks. A circuit is thereupon established from the tip of plug 224 over the No. 4 upper contacts of relay 233, conductor 238, the No. 4 upper back contact of relay 333, conductor 334, the lower left normal contacts of splitting key 2|3, the lower back contact of relay 2| 3, conductor 2 |5, thence as previously traced to ground through the winding of relay ||2 and through the primary winding of transformer ||-4. It will be assumed that the trunk terminating in jack 430 tests idle and that the operator on receiving no busy click in her headset inserts the plug 224 into jack 43D. A circuit is thereupon established from ground through the high and low resistance windings of sleeve relay 49| in series over the sleeves of jack 43|) and plug 224, the No. 3 upper alternate contacts of relay 233 to battery through the windings of relays 2|9 and 223. Sleeve relay 43| operates in this circuit establishing an obvious circuit for relay 432 which operates establishing a loop circuit over the two-conductor trunk extending to the terminating oilice and terminating thereat in an incoming selector. This loop circuit may be traced from battery at the terminating oilice through the lower winding of relay 433, the lower back contact of relay 434, the lower left Winding of repeating coil 435 over the interoce trunk conductor 446, the lower right winding of repeating coil 43?, the contacts of relay 442, the winding of relay 438, the upper right winding of coil 437|, trunk conductor 439, the upper left winding of repeating coil 435, the upper back contact of relay 444 and through the upper winding of relay 483 to ground. Relays 433 and 408 both operate, relay 423 closing an obvious circuit for relay 4H! and relay 408 connecting direct ground through the upper or low resistance winding of relay 43| to the previously traced sleeve circuit thereby operating both relay 2|9 and relay 223 at the operators position circuit.

Relay 4| upon operating establishes an operating circuit for relay 444 extending from battery through the winding thereof, over the back Contact oir relay 4|| to ground over the upper contacts of relay 4| El whereupon relay 434 operates to open the previously traced loop circuit through the windings of relays 433 and 438. Relay 433 does not release, however, being held operated in a local circuit through both of its windings and over the front contact of relay 434. Relay 4,38, however, releases again removing low resistance ground from the trunk sleeve circuit thereby releasing marginal sleeve relay 2 I9. Relay 2|$` therefore operates only momentarily and without effect at this time.

Relay 223 upon operating establishes an obvious circuit for relay 2|8 which at its upper front contact connects ground through high resistance 22| over the No. 2 upper contacts of relay 233.110 the circuit .of calling supervisory lamp 222 for warming such lamp without `lighting Vit to improve its flashing characteristic and establishes a Vtalking circuit from the tip conductor 4|2 of the outgoing trunk, over the tips of jack 440 and plug 224, the No. 4,v upper front contact of relay 263, conductor 238, the No. 4 upper back contact of relay 333, conductor 364, the lower left contacts of splitting key 2|6, the inner lower front contact of relay 2| 8, the lower back contact of relay 223, conductor H5, thence as traced to the operators telephone circuit and returning o-ver conductor 1, the upper back contact of relay 223, the inner upper front contact of relay 2|3, the upper left normal contacts of key EIS, conductor 305, the No. 2 lower back contact of relay 3,03, conductor 201, the No. 4 lower front contact of relay 243 over the rings of plug 224 and jack 433 to the ring conductor 413 of the outgoing trunk. At its lower back contact relay 2|3 opens the busy test circuit previously traced.

Relay 4|0 upon operating also closes a circuit extending from battery vthrough the winding of relay 4|4, thence over the lower contacts of relay 4||l over the normal or position contacts of sequence switch cam 4|5 to ground, whereupon relay 4|4 operates, locks in a circuit from battery through its winding, over the lower contacts of relay 4| 3 and to ground over its own lower contacts and connects ground to the start circuit for starting a preselected idle link circuit such as is represented by the box 4|3 and which is fully disclosed in the patent to J. F. Dahl 2,020,458 of Nov. 12, 1935, whereupon the trunk finder 4H of the link circuit is started in search of the calling trunk.

As soon as the trunk is found, the link circuit sequence switch is advanced thereby causing the advance of the sequence switch of the incoming selector into position I8 and the selector 4| 8 of the link circuit is started in search of an idle key-pulsing receiving circuit such as is indicated by the box 4| 9. When the selector 4|8 finds an idle receiving circuit, a test relay in the link circuit operates to arrest the hunting movement of the selector and to advance the sequence switch of the link circuit. A circuit is thereupon established which may be traced in part from battery through thelower winding of supervisory relay 423 vin the incoming selector, through the lower right winding of repeating coil 4535., over the contacts of sequence switch cam 42|, over the ring talking conductor extending through the link circuit to the receiving circuit 419, thence through the high and low resistance windings of a relay (not shown) returning over the tip conductor extending from the receiving circuit through the link circuit, over the contacts of cam 422 through the upper right winding of repeating coil 435 to ground through theY upper winding of` relay 420. Due to the inclusion of the high resistance winding of the relay in the receiving circuit,` the marginal supervisory relay 423 does not operate. At the receiving circuit a condition is established which causes the sequence switch of the link circuit to advance to a position for starting the sender selector 423 in search of an idle sender such as is indicated by the box 424. When an idle sender has been seized by the link circuit, a signal is transmitted from such sender to the receiving circuit whereby the high resistance winding of the supervisory relay thereof becomes shunted and the super- Visory relay 420 inthe incoming selector circuit thereupon operates.

Relay 420 upon operating closes the circuit of relay 411 which may be traced from battery through its winding and lower normal contacts, over the contacts of relay 420 to ground over the upper contacts of relay 410. Relay 411 locks over its lower alternate contacts to ground at the lower contacts of relay 414 and opens the circuit of relay 404 which releases to restore the loop circuit through the winding of relay 408. Relay 408 now operates and reconnects low resistance ground to the sleeve of the trunk through the upper or low resistance winding of sleeve relay 401. In response to the increased current now flowing over the sleeve circuit previously traced through the windings of relays 219 and 220, marginal relay 219 now operates to connect ground over its contacts through resistance 225, the No. 2 upper contacts of relay 203 to the supervisory lamp 222 whereupon such lamp lights as a signal to the operator that a sender has become associated with the extended connection.

Since the call is an inward call, the operator may depress the front cord key-pulsing key 306 as soon as she has plugged up the cord whereupon a circuit is established from ground over the No. 3 upper back contact of relay 300, conductor 311, lower front contact of relay 213, conductor 309, over the right contacts of key 301i thence in parallel through the winding of relay 301 and the non-inductive resistance 308 to battery and a circuit is also established from battery through the winding of relay 303, left contacts of key 300,

conductor 309, lower contacts of relay 218, con- Y ductor 311 to ground at the No. 3 upper back contact of relay 300. Relays 301 and 303 both operate, relay 301 upon operating extending its operating ground over its lower contact, the upper back contact of relay 314 and the upper front contact of relay 391 to battery' through the winding of relay 312. Relay 312 thereupon operates and locks itself from ground on conductor 309, over the No. l upper contacts of relay 303, over its own upper contacts, the normal contacts of relay 313 and through its own inner lower front contact and winding to battery and extends this locking circuit from its upper contacts through the No. 1 lower contacts and winding of relay 303 to battery. Relay 303 upon operating causes lamp 315 to light in a circuit through resistance 316 and over its No. 3 upper contacts and at its No. 4 lower contacts prepares the circuit for relay 314. Relay 301 is now held operated under the control of relay 314 over a circuit extending from battery through its winding and outer lower contact, over the upper back contact of relay 314 and the No. 1 upper contact of relay 303 to ground on conductor 309.

As soon as a sender has become connected to the link circuit and such connection has been signaled by the operation of sleeve relay 219, a circuit is established from ground over its contacts, conductor 343, the No. 4 lower contacts of relay 303, the inner lower contacts of relay 301 to battery through the winding of relay 314. Relay 314 operates, opening the locking circuit of relay 301 at its upper back contact and establishing a circuit over which a key-pulsing signal is transmitted which may be traced in part from the signaling current supply circuit 350, over conductor 318, through resistance 320, the upper front contact of relay 314, through the right windings of repeating coil 311, the lower front contact of relay 314, resistance 321 and conductor 319, to the supply circuit 350. With relay 303 operated, the current impressed upon the left windings of repeating coil 311 is transmitted to the receiving circuit over the cord circuit and trunk, by way of a circuit which may be traced from the upper terminal of the left windings of repeating coil 311 over the No. 4 upper front contact of relay 303, conductor 208, the No. 4 upper front contact of relay 203, tips of plug 224 and jack 400, tip trunk conductor 412 through the left windings of repeating coil 401 returning over trunk conductor 413, rings of jack 400 and plug 224, the No. 4 lower front contact of relay 203, conductor 201, the No. 2 lower front contact of relay 303, to the lower terminal of the left windings of repeating coil 311. The current is further inductively transmitted over conductors 406 and 409 of the interofce trunk through the right windings of repeating coil 401 and the left windings of repeating coil 405 and is inductively transmitted to the key-pulsing receiving circuit 419, through the link circuit 410. Following the operation of relay 314 and the opening of the holding circuit of relay 301 thereby, relay 301 releases after a predetermined interval if the key-pulsing key 390 has been released, and relay 301 upon releasing causes the release of relay 314 to terminate the key-pulsing signal. With both relays 301 and 314 released a circuit is established from ground over the lower contacts of relay 312, the lower back contact of relay 314 and the upper back contact of relay 301 to battery through lamp 360 which is lighted as a signal to the operator that she may proceed with the keying of the desired line number on the key-set 310.

As previously stated, signaling current of six frequencies is applied from the circuit indicated by the box 350 disclosed in the lower portion of Fig. 3. The six frequencies are generated by six vacuum tube oscillator circuits and are applied in different combinations of two frequencies each to twelve pairs of signaling conductors, shown extending upwardly from the box 350, by equipment fully disclosed in the aforementioned application of P. B. Murphy. One of the combinations of frequencies is employed in the transmission of the preliminary key-pulsing signal previously referred to, ten of the combinations of frequencies are employed in the transmission of the digit values 0 to 9, inclusive, and one of such combinations is employed in the transmission of a nal start signal. Preferably the frequencies are of '700, 900, 1100, 1300, 1500 and 1'100 cycles, respectively and are applied in the combinations set forth in the following table for the several signals above mentioned:

Code signals Frequency 0 l 2 3 4 5 6 7 8 9 KP ST x x x x x x x x x x x x x x x x x x x x x x x x At the receiving circuit, the key-pulsing signal of the two frequencies 1300 and 1700 is instrumental in preparing the receiving circuit to receive signals transmitted through the subsequent operation of the keys of the key-set 31'0. It will be assumed that the num'ber of the desired line is 2369 and that the operator after seeing the lighted lamp 380, proceeds with the keying of the desired line number on the key-set 310 and first momentarily operates the digit key 328 of lher key-sety to cause the transmission ofa signal for the thousands digit 2. Referring" to the preceding table it will be noted that Yfor thisdigt the signaling supply circuit 350 supplies current of the two frequencies 900'and 1300 cyclesto the circuit which may be tra-ced from conductor l32 2, through resistance 324, the left contacts of the depressed Akey 328, over the inner upper back contact of relay 3I4, through the right windings of repeating coil 3 I 1, over the inner lower hack contact of relay 314, the right contacts of key 328,

'resistance 325 thence over conductor 32-3--to the supply circuit 350 so long as the key 328 is 'held depressed. AsV before this signalling current is indu'etively impressed over the windings of repeating coil 3l 1 and the circuits previously traced and is effective at the receiving circuit to cause the registration of the digit 2 on the thousands register of the associated' sender 424.

The operator will next momentarily depress the digitV key 323 to cause the transmission cfa signal for the hundreds digit 3. Referring, to the preceding table, it will be noted thatV for Vthis digit the signaling supply circuit V350 supplies current of the two frequencies 1300- and 1500 cycles to the circuit which may be traced' from the supply circuit 350, over conductor 323, through resistance 321 over the left contacts of the depressed key 329, over the inner upper Iback contact of relay through the right windings of repeatingcoil 311, over the inner lower back. contact 'ofrelay 314, over the right contacts of key 320,y through resistance 330' and over conductor 33| to the supply circuit 350 so long as the key 320is held T depressed. As before this signaling current is inductively impressed over the windings of repeating coil 311 and the circuits previously traced and is effective at the receiving circuit to cause the registration of the digit 3 on the hundreds regis.- ter of the associated sender.

The operator will next momentarily depress the digit key 332 to cause the transmission of a signal for the tens digit 6. Referring to the preceding table, it will be observed that for this digit the signaling supply circuit 350 supplies current of thetwo frequencies 700 and 1100 cycles to the circuit which may 'be traced from conductor 333, through resistance 334 over the left contacts of the depressed key 332, over the inner upper back contact of relay 314, through the right windings of repeating coil 3|"I,- over the inner` lower back contact of relay 3114, the right contacts of. key 332', through resistance 335 and over conductor 336 to the supply Vcircuit 350 so long as the key 332 is held depressed. As before, this signaling' current is inductively impressed over the wind.- ings of repeating coil' 3H and the circuits previously traced and is effective at the receiving circuit to cause the registration of the digit 6 on the tens register of the associated sender.

The operator will next momentarily depress the digit key 331 to cause the transmission of a signal for the units digit 9. Referring to the preceding table it will be seen` that for this digit the sig-naling supply circuit 350 supplies current of the two frequencies '100 and 1500 cyclesv to the, circuit whichmay be traced from conductor 338, through resistance 339 over the left contacts of the depressed key 331, over theV inner upper back contact of relay 314, through the right windings of repeating coil 3.1.1, over the inner lower Iback contact ofrelay 314, the right contacts of key 331, through resistance 340 and over conductor34lto the supply circuit 35.0- so long as the key 331 is rent is inductively impressed over the windings of 'repeating coil 3|1 and the circuits previously traced and is elective at the receiving circuit to cause `the registration of the digit 9 on the unit `register of'the Vassociated sender.

Had the operator keyed digits having values other than 'those discussed, signals of combined frequencies would have been transmittedY in accordance with the preceding table and in the manner previously described;

Following the keying of the last or units digit onthe key-set 3|0, the operator momentarily de- Ypresses the startV key 342 thereby 'closing an obvious circuit over thek alternate contacts' of such key for start rel-ay 3t3 vwhich operates and locks over'itsinner upper front contact to ground at the lower `front contact of' relay 3'I'2` and at its upper transfer contacts transfers the holding circuit for relay 3|2 from ground at the No. 3 upper back contact of relay 300 to ground over theY left contacts of key 3'421s'o that relay 3|2 is now maintained Operated under the controly of key 342. Relay 3T3 also establishes a newV holding circuit for-relay 303 `extending from battery' through the winding'ofsuch relay, over the No. l lower contacts thereof, the upper contacts of 'relay 313, the Njo. lupper contacts of relay 303, conductor 309, the lower contacts of relay 2I8 and conductor3il to ground at the No'. 3 4upper back'contact of relay 300. At its 'lower front contact relay 313 connects' non-inductive resistance 343 in parallel with the winding of relay 3 l 2 to render it' slow to release and at its other lower front contacts establishes a signaling circuit from the signaling supply circuit' 350 `over conductor 344', through resistance 345, the inner lower front contact of relay 313, over the inner lower back contact of relay 3M', through the right windings of repeating coil 3H, over the inner upper back contact of` relay 314, the middle 'lower front contact of relay 313, resistance 346 and conductor 341 tothe signaling supply circuit 350'. Hence in accordance withfthev preceding table, current of the two frequencies 1500 and 1700 cycles is supplied to this circuit and current of such frequencies is inductively impressed over the windings of repeating co'il` 3| 1 and the circuits previously traced and may be effective at the receiving' circuit to inform the sender thattno" further digit signals' are' to be expected.

As s'ogon as the operator releases the key 342, relayv 312 releasesA followed after an interval by the release of relays 3|'3 andV 303. The operators key-set circuit is now restored to its normal con.- dition. Sincel the present invention does not involve the supervisory featuresY of the cord circuit and ofv the, position circuit, no detailed description thereof will be given herein.

Should the operator desire to key-pulse out over; thev rear cord; plug 200 of her cord circuit `she would operate the rear cord pulsing key 354 instead' of the key-pulsing key 305'. Upon the operation of key 354', relay` 301 is operated as beforel and a circuit is established for relay 300 which. may be traced from battery through its winding, over the left contacts of key' 354, conductor 355, the inner lower contacts of relay 212 and conductor 355 to ground at the No. 2 upper fbackcontact ofrelay 303, Relayv 331 upon operground on conductor 355 over the No. l upper contacts'of relay 300, over its own upper contacts, the normal contacts of relay 313 and through its own inner lower front contact and winding to battery and extends this locking circuit from its upper contacts through the No. l lower contact and winding or' relay 300 to battery.

Relay 300 upon operating closes a circuit for lamp 351 through resistance 315 and over its No. l upper contacts and at its No. 4 lower contacts prepares the circuit for relay 314. Relay 301 is now held operated under the control of relay 314 over a circuit which may be traced from battery through its winding and outer lower contact over the upper back contact of relay 314 and the No. 1 upper contacts of relay 300 to ground on conductor 355. When thereafter relay 210 operates to indicate that a receiving circuit and sender have become attached to the trunk with which cord plug 200 has been connected, the circuit of relay 314 may be traced from ground over the contacts of relay 210, conductor 349, the No. l lower contacts of relay 300, over the inner lower contacts of relay 301 to battery through the winding of relay 314. Relay 314 thereupon operates to apply the key-pulsing signaling current over conductors 318 and 319 and through the right windings of repeating coil 311 as previously described, which circuit is nductively connected to a circuitl which may be traced in part from the tip of plug 200 over the No. upper contacts of relay 203, conductor 205, the No. 2 upper front contact of relay 300, through the left windings of repeating coil 311, the No. 3 lower front contact of relay 300, over conductor 209 and the No. 5 lower contacts of relay 253 to the ring of plug 200. Relay 314 upon operating also opens the holding circuit of relay 301 which releases aiter an interval opening the circuit of relay 314 which then releases to discontinue the key-pulsing signal. From this point the key-set circuit functions in the manner previously described eXcept that with relay 300 operated rather than relay 303, all of the keyed digit signals and the nal start signal are transmitted over the plug 200.

The embodiment of the invention disclosed in Figs. 5 and 6 will now be considered. It will be assumed that a toll call is incoming to the operators position and that the operator answers the call on the toll line by plugging the plug 500 of a cord circuit of her position into the toll line jack 50|, thereby establishing a circuit from high resistance ground over the sleeves of jack 501 and plug 500, thence through non-inductive resistance 502 to battery and in parallel with such resistance through the windings of relays 503, 504 and 505 in series to battery. Due to the high resistance of the sleeve circuit of the toll trunk, marginal relays 503 and 504 do not operate, but relay 505 operates closing an obvious circuit for relay 506 which operates to transfer the tip of plug 500 from the busy test lead 501 of the associated position telephone circuit to the normal contacts of the ringing key 508. When now the operator throws the key 509 to its left or talking position, a talking circuit is established from the toll trunk over the tips of jack 501 and plug 500, the front contact of relay 505, the upper normal contacts of ringing key 558 and cord splitting key 510, the upper alternate left contacts of key 509, the inner upper right normal contacts of grounding key 51 I, conductor 512, the lower normal contacts of relay 600, conductor 513, the left windings of repeating coil 514, the non-inductive resistance 515, conductor 516, the upper normal contacts of Arelay 600, conductor 511, the inner lower right normal contacts of grouping key 51|, the lower left alternate contacts of key 509,Y the lower normal contacts of keys 510 and 508 over the rings of plug 500.and jack 501.

At the operators telephone circuit, this circuit is inductively connected through the right winding of repeating coil 514, over the tips of headset jacks 518 and 513 and head-set plugs 520 and 521 through the headset transmitter 522 and is inductively connected to the headset receiver 523 over the sleeves of plug 520 and jack 518, the inner lower back contact or relay 524, through resistance 515, the lower left winding or' repeating coil 5I4, the upper back contact ol relay 524, and the rings of jack 510 and plug 52|. The operator is now enabled to receive instructions over the toll line for terminating the connection.

It will be assumed that the connection is to be terminated in the dial switching oiiice schematically disclosed in Fig. 4. The operator will first test the jacks of trunks extending to such oilice by touching the tip of cord plug 525 to the sleeves of such jacks. The sleeves of busy trunks will have battery potential connected thereto whereby a busy test circuit will be established extending from the tip of plug 525, over the back contact of relay 526, busy test lead 501, upper right normal contact of grouping key 5I I, through the winding of busy test relay 521 at the operators telephone circuit to ground. Relay 521 will therefore operate connecting battery through the parallelly connected condenser 528 and resistance 529 through the primary winding of busy test coil 530 to ground whereby current is induced into the operators headset receiver to produce a busy test click, over a circuit extending through the secondary winding of coil 530 over the inner lower back contact of relay 524, thence as traced through the headset receiver 523 and over the upper back contact of relay 524. When, however, the operator tests the jack of an idle trunk, relay 521 will not operate to produce a click in the headset receiver and thereupon the operator will insert the cord plug 525 into the idle trunk jack.

It will be further assumed that the idle trunk is the one disclosed in Fig. '4 as terminating in jack 450 at the toll operators position and extending to the terminating office where it terminates in an incoming selector of the type schematically disclosed in the right portion of Fig. 4. Upon the insertion of the plug 525 into jack 450, a circuit is closed fromy -ground over the sleeves of the jack and plug to battery through the winding of cord sleeve relay 53| which thereupon operates and closes an obvious circuit for relay 526, which thereupon operates to transfer the tip of plug 525 from its normal connection with busy test lead 501, into connection with the upper normally closed contacts of ringing key 532. A circuit is now established from ground through the upper winding of relay 403 over the upper back Contact of relay 404, the upper left winding of repeating coil 405, tip conductor 451 of the interoice trunk, tips of jack 450 and plug 525, the front contact of relay 526 through the upper winding of retard coil 533, winding of supervisory relay 534, lower winding of coil 533, rings of plugr525 and jack 450, ring conductor 452 of the interoflice trunk, lower left winding of repeating coil 405, the lower back contact of relay 404 to battery through the lower winding of relay 403. Relays 403 and 534 both operate in this circuit, but as previously described, relay 403 upon operating causes the operation of relays H and 404 whereby the loop. supervisory circuit just traced is immediately opened to release relay 534. Relay 534 is therefore operated only momentarily at this'time and without effect. Aiter the loop circuit is opened, relay 403 is maintained operated locally `over the front contact of relay 404 as previously described and causes the operation and locking of relay M4 to close a ystart circuit for a preselected idle link circuit such as is represented by the box `M6.

The link circuit then proceeds to connect with the calling trunk, with an idle receiving circuit and with an idle sender. As .previously described when an idle sender has been selected, relay 4l I at the incoming selector is operated, to release relay 4011 whereupon the loop circuit previously traced through the windings of relays 403-and 534 is reestablished. Relay v531i thereupon operates to close the circuit of supervisory lamp 535 as a signal to the operator that a sender has been seized and that she may proceed to key the number of the desired line. She rst operates the cord key 5&0 to open the cord Ycircuit toward the toll line and then operates the key-pulsing key 606 of her key-set circuit. Upon the operation of key 606 an obvious circuit is established from ground over the left contacts of key 606 through the winding of the key-pulsing relay 601 and through the non-inductive resistance 608 in parallel to battery and a'second circuit is established from ground over the right contacts of key 606 through the winding of relay 600 and resistance 60| to battery and in parallel therewith over the inner upper normal contacts of relay 613 to battery through the winding of slow-torelease disconnect relay SI2. Relays 600, 601 and 'SI2 all operate, relay 6l2 locking under the control of relay 6I3 in a circuit from battery through its winding over the inner upper normal contacts of relay 6 i 3 to ground at the inner lower front contact of relay 6I2, and holding relay 600 operated over its inner lower front contacts following the release of key 606. When key 606 is released, relay 601 releases after a predetermined interval and with relay 6l2 locked oper-ated establishes a circuit extending from battery through lamp 650 the lower contacts of relay 6|2 to ground over the back contact of relay 601 whereupon lamp 650 lights as a signal to the operator that she may proceed to key up the digits of the wanted line designation on the keys of her key-set 6|0.

During the period that relay 601 remains operated, key-pulsing signaling current of the two frequencies 1300 and 1700 cycles is transmitted from the signaling current supply circuit 650 over conductor 6|3, resistance 620, the lower contact of relay 601, the right windings of repeating coil 6|1, the inner lower contacts of relay 661, through resistance 62| and over conductor 659 to the supply circuit 650. This current is inductively transmitted over a circuit which may be traced from the upper terminal of the left windings of repeating coil 6l1, over the lower front contacts of relay 600, conductor 5|2, the inner upper right normal contacts of grouping key 5H, the upper left alternate contacts of talking key 509, upper normal contacts of splitting key 536 and ringing key 532, thence as traced over the interoime trunk circuit through the left windings of repeating coil 405 and returning over the lower normal contacts of keys 532 and 536, the lower left alternate contacts of key 509, the inner lower right normal contacts uppenfrcnt contacts of relay 600, to the lower terminal of the left windings .of repeating coil SI1. As before described the signaling current is further vtransmitted through the windings of repeating coil 405130 the receiving .circuit 410.

After observing the lighted lamp 650, the operator proceeds tokey the digitsof the vwanted line number in the manner .previously described,

following which .she ,depressesthe start key 642, whereupon a circuit is established from ground lover the right Ycontacts of key 6.4.2 through the winding of start vrelay 6l3 and resistance 6M to battery. Relay 6.13 thereuponoperates, closes a locking circuit foritseli over its inner lower front contacts to ground over the inner .lower front contacts ci relay 612 and .transfers the holding circuit of relay ;6I2 tothe control of key 642. This holding circuit may ,be traced from battery through the winding of relay 612, over the inner upper alternate contacts of relay 6I3 to ground over the left contacts of key .642, Relay 613 is thus maintained operated so long as the key 642 is held depressed, `butfupon the release of the key,

releases aiter a predetermined rinterval in turn Areleasing relays 600 and BIB. VDuring the time that relay'ilBiis thus operated, start signaling current of the two frequencies 1500 and 1700 cycles is transmittedfrom the supply circuit 650 over conductor 644, through resistance 6115, over the ,upper front contacts of Yrelay SiS, through the right windingsof repeatingcoil 6I1, over the lower front contacts of relay ,6.13, through resistance 666 and conductor ,641 to the supply circuit 650 and thence inductively to the receiving circuit. The operators key-set vcircuit is now restored to its normal condition. Since the invention doesnot concern the'supervisory or other functions of the .cord and `position circuits, a

`further description thereof will not be given herein.

Had the operator desiredto key-pulse out over keys, a key-pulsing key, a start key, a plurality of sources of signaling current, a first relay operable in response to the operation of said keypulsing key to establish a signaling circuit from of grouping key 5H, conductor ,5H over Ythe 75 said key-set circuit to said cord circuit, a second relay operable following the operation of said key-pulsing key to associate one of said sources of signaling current with said signaling circuit as a signal that key-pulsing has been initiated, means effective upon the operation of said digit keys for selectively associating others of said sources of signaling current .with said signaling circuit, a relay responsive to the operation of said start key for associating another of said sources of signaling current with said signaling circuit as a signal that key-pulsing has been completed, and means operative a predetermined interval followingthe restoration of saidV start key for releasing said relays to restore said key-set circuit to normal.

2. In a telephone system, a cord circuit and an operators key-set circuit comprising digit keys, a key-pulsing key, a start key, a plurality of sources of signaling current, a first relay operable in response `to the operation of said key-pulsing key to establish a signaling circuit from said keyset circuit to said cord circuit, a second relay operable following the operation of said key-pulsing key to associate one of said sources of signaling current with said signaling circuit as a signal that key-pulsing has been initiated, a lamp signal operable following the release of said keypulsing key and said second relay for indicating that the digits of a wanted line number may be keyed on said digit keys, means effective upon the operation of said digit keys for selectively associating others of said sources of signaling current with said signaling circuit, a relay responsive to the operation of said start key for yassociatinganother of said sources of signaling current with said signaling circuit as a signal y that key-pulsing has been completed, and means operative a predetermined interval following the release of said start key for releasing said relays to restore said key-set circuit to normal.

3. In #a telephone system, a cord circuit, an

operators telephone circuit and a key-set circuit comprising digit keys, a key-pulsing key, a start key, a plurality of sources of signaling current, a first relay operable in response to the operation of said key-pulsing key to disconnect said operators telephone circuit from said cord circuit and to establish a signaling circuit from said key-set circuit to said cord circuit, a second relay operable following the operation of said keypulsing key to associate one of said sources of signa-ling current with said signaling circuit as a signal that key-pulsing has been initiated, means effective upon the operation of said digit keys for selectively associating others of said sources of signaling current with said signaling circuit, a relay responsive to the operation of said start key for associating another of said sources of signaling current with said signaling circuit as a signal that key-pulsing has been completed and means operative a predetermined interval following the restoration of said start key for releasing said relays to restore said key-set circuit to normal.

4. In a telephone system, a cord circuit, and a key-set circuit comprising digit keys, a keypulsing key, a plurality of sources of signaling current, a iirst relay operable in response to the operation of said key-pulsing key to establish a signaling circuit from said key-set circuit to said cord circuit, a second relay operable during the operation of said key-pulsing key and for a predetermined interval following the release of said key to associate one of said sources of signaling current with said signaling circuit as a signal that key-pulsing has been initiated, a start relay, a slow-to-release relay operable in response to the operation of said key-pulsing key to lock itself operated under the control of said start relay and to hold said first relay operated following th'e release of said key-pulsing key, means effective upon the operation of said digit keys for selectively associating others of said sources of signaling current with said signaling circuit, and a start key effective upon its operation for operating said start relay to associate another of said sources of signaling current with said signaling circuit as a signal that key-pulsing has been completed and for transferring the locln'ng circuit of said slow-to-release relay to the control ,of said start key, said start relay upon operating locking under the control of said slow-to-release relay whereby'upon the release of said start key, said slow-to-release relay in turn releases said other relay to open said signaling circuit.

5. In a telephone system, a first office, a second office, a trunk interconnecting said oiiices, a cord circuit at said rst office for connection with said trunk, signal receiving equipment at said second office associable with said trunk, a key-set circuit associable with said cord circuit comprising digit keys, a key-pulsing key, a start key, a plurality of sources of signaling current, a rst relay operable in response to the operation of said key-pulsing key to establish a signaling circuit from said key-set circuit to said receiving equipment, a second relay operable in response to the association of said receiving equipment with said trunk for associating one of said sources of signaling current with said signaling circuit as a signal that key-pulsing has been initiated, means effective upon the operation of said digit keys for selectively associating others of said sources of signaling current with said signaling circuit, a relay responsive to the operation of said start key for associating another of said sources of signaling current with said signaling circuit as a signal that key-pulsing has been completed, and means operative a predetermined interval following the restoration of said start key for releasing said relays to restore said key-set circuit to normal.

6. In a telephone system, a first office, a second oflice, a trunk interconnecting said ofces, a cord circuit at said first ofce for connection with said trunk, signal receiving equipment at said second oflice associable with said trunk, a key-set circuit associable with said cord circuit comprising digit keys, a key-pulsing key, a plurality of sources of signaling current, a first relay operable in response to the operation of said key-pulsing key to establish a signaling current from said key-set circuit to said receiving equipment, a keypulsing relay, a first slow-to-release relay operable in response to the operation of said keypulsing key to lock itself operated under the control of said key-pulsing relay and to prepare an operating circuit for said key-pulsing relay, a start relay, a slow-to-release disconnect relay operable in response to the operation of said first slow-to-release relay to lock itself operated under the control of said start relay and to hold said rst relay operated, means operable upon the association of said receiving equipment with said trunk to complete the operating circuit of said keypulsing relay whereby said key-pulsing relay releases said rst slow-to-release relay which in turn releases said key-pulsing relay and whereby, during the interval that said key-pulsing relay is maintained operated, one of said sources of signaling current is associated with said signaling circuit as a signal that key-pulsing has been initiated, means effective upon the operation of said digit keys for selectively associating others of said sources of signaling current with said signaling circuit, and a start key effective upon its operation for operating said start relay to associate another of said sources of signaling current with said signaling circuit as a signal that key-pulsing has been completed and for transferring the locking circuit of said disconnect relay to the contacts of said start key, said start relay upon operating, locking under the control of said disconnect relay whereby upon the release lof` said start key, said disconnect relay releases after an interval in turn releasing said first relay and said start relay to open said signaling circuit.

7. In a telephone system, a cord circuit having front and rear sections and a'n operators keyset circuit comprising digit keys, a front cord key-pulsing key, a rear cord key-pulsing key, a start key, a plurality of sources of signaling current, a first relay operable in response to the operation of said front cord key-pulsing key for establishing a signaling circuit from said key-set 10 circuit to the front section of said cord circuit, a second relay operable in response to the operation of said rear cord key-pulsing key for establishing a signaling circuit from said key-set circuit to the rear section of said cord circuit, a third relay operable following the operation of said key-pulsing key to associate one of said sources of signaling current with said signaling circuit as a signal that key-pulsing has been ini- 'tiatecL means effective upon the operation of said digit keys for selectively associating others of said sources of signaling current with said signaling circuit, a relay responsive to the operation of said start key for associating another of said sources of signaling current With said signaling circuit as a signal that key-pulsing has been completed and means operative a predetermined interval following the restoration of said start key for releasing said relays to release said key-set circuit to normal.

JAMES B. MCKIM. 

